Fusashi Miyahara

Progress of 7-GeV SuperKEKB Injector Linac Upgrade and Commissioning

KEK injector linac is being upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. Electron beams will be generated by a new type of RF gun, that will inject a much higher beam current to correspond to a large stored beam current and a short lifetime in the storage ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced by introducing a damping ring, followed by the bunch compressor and energy compressor. The recent status of the upgrade and beam commissioning is reported.

Preliminary design of FCC-ee pre-injector complex

The design of a 100 km circular e + e − collider with extremely high luminosity is an important component of the global Future Circular Collider (FCC) study hosted by CERN. FCC-ee is being designed to serve as Z, W, H and top factory, covering beam energies from 45.6 to 175 GeV. For the injectors, the Z-operation is the most challenging mode, due to the high total charge and low equilibrium emittance in the collider at this energy. Thus, fulfilling the Z-mode will also meet the demands for all other modes of FCC-ee. This goal can be achieved by using a 6 GeV NC linac with an S-band RF frequency of 2.856 GHz and a repetition rate of 100 Hz. This linac will accelerate two bunches per RF pulse, each with a charge of 6.5 nC. Positrons will be generated by sending 4.46 GeV e − onto a hybrid target so that the e + created can still be accelerated to 1.54 GeV in the remaining part of the same linac. The emittance of the e + beam will then shrink to the nm level in a 1.54 GeV damping ring. After damping, the e + will be reinjected into the linac and accelerated to 6 GeV. The e − and e + will then be accelerated alternately to 45.6 GeV in the booster, before they are injected into the collider.

Emittance Growth by Misalignments and Jitters in SuperKEKB Injector Linac

SuperKEKB injector linac have to transport high-charged beam with low emittance to SuperKEKB ring for high luminosity, 8 × 1035. For the low emittance, photocathode RF gun was adopted as electron source. One of the main reason of the beam emittance blow-up electron linac is generally induced by wakefield in acceleration cavities. A charged beam with a offset from a center of a cavity is affected by the wakefield depending on the offset size in the acceleration cavity and the beam emittance is increased. This emittance blow-up can be eliminated by appropriate steering magnet control so as to cancel the wake effect in the acceleration cavity. We perform particle tracking simulation with some misalignments and beam jitter. Emittance growth by the misalignments and the beam jitter is evaluated in this report.

Commissioning of the Phase-I SuperKEKB B-Factory and Update on the Overall Status

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning and beam related background measurements were performed in this phase. Low emittance tuning techniques have also been applied in order to set up the rings for Phase-2 with colliding beams next year. An update of the final focus system construction, as well as the status of the injection system with the new positron damping ring and high current/low emittance electron gun is also presented.

Pulse-to-Pulse Modulation of Injector Linac with Event Timing System

The Pulse-to-Pulse Modulation of Injector Linac at KEK is developed for efficient injections. It automatically switches the beam mode with the real-time process. We integrated this system in 2009 to simultaneously perform the top-up filling into more than one rings with only one injector. The system is based on the Event Timing System. Recently, we upgraded the configuration of Event Timing System to satisfy the complicated requirements of SuperKEKB and developed the test procedure to understand stability of real-time process. The failure of real-time process at Main Trigger Station is intentionally caused when we shorten the allowed computing time as the stress test. The reasonable dependence between the failure rate and the allowed computing time is determined. It indicates we can evaluate the failure rate in case of normal operation at Main Trigger Station.